Work in progress seeks to define the role of pilus-like colonization factors of enterotoxigenic E. coli in human acute diarrhea. Previous work demonstrated that a strain of enterotoxigenic E. coli (H-10407) possesses a heat-labile antigen (colonization factor, or CF) with fimbriate morphology. Doses of 10 to the 5th power of this strain colonized the small intestine of the infant rabbit with concomitant diarrhea while derivatives of this strain lacking CF were ineffective. In current work a procedure has been developed for purification of this antigen. The antigen is removed from agar-grown bacteria by agitation. Purification was achieved by isoelectric precipitation and differential ultracentrifugation. Antiserum prepared against this antigen was found to be specific for CF, agglutinating living but not heat-killed enterotoxigenic E. coli of many different serotypes. This serum is currently being used to assess the frequency of CF among enterotoxigenic E. coli obtained from diarrhea cases in the US and in Mexico and also among enterotoxigenic and non-enterotoxigenic isolates obtained from healthy subjects. An epidemic strain of ST-only E. coli associated with a nonsocomial outbreak in Houston was shown to possess this antigen. Enterotoxigenic strains possessing CF were shown to adhere preferentially to the upper half of the small intestine of the infant rabbit while those lacking CF did not adhere. Current work continues the assessment of the significance of CF in human enterotoxigenic E. coli diarrhea. For this purpose we are actively involved in the development of techniques for determining humoral antibody response to CF antigen. BIBLIOGRAPHIC REFERENCES: DuPont, H.L., J. Olarte, D.G. Evans, L.K. Pickering, E. Galindo and D.J. Evans 1976. Comparative susceptibility of Latin American and United States students to enteric pathogens. N. Engl. J. Med. 295:1520-1521. Ryder, R.W., I.K. Wachsmuth, A.E. Buxton, D.G. Evans, H.L. DuPont, E. Mason and F.F. Barett. 1976. Infantile diarrhea produced by heat-stable enterotoxigenic Escherichia coli. N. Engl. J. Med. 295:850-853.